Tuning a programmable power line filter

ABSTRACT

Tuning a programmable power line filter, the power line filter including a live line, a neutral line, and a ground line connected to input terminals of the filter on an input side of the filter, the live line and the neutral line connected through inductors in the filter to output terminals on an output side of the filter, X-capacitors selectably connected through tuning switches between the live line and the neutral line, Y-capacitors selectably connected through tuning switches between the live line and ground and/or between the neutral line and ground, and a tuning control circuit connected to the tuning switches and selectably connected through one or more programming switches to the load, including measuring by the tuning control circuit the input impedance of the load and programming by the tuning control circuit the tuning switches in dependence upon the input impedance of the load.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The field of the invention is data processing, or, more specifically,methods, apparatus, and products for tuning a programmable power linefilter.

2. Description of Related Art

A challenge for marketability of information technology equipment is thedifficulty of meeting safety and electromagnetic compatibilityregulatory requirements as mandated by many worldwide governingregulatory bodies. One such requirement, and of particular interest in apower supply is its electromagnetic interference (EMI) profile. For thisreason, power supply designs often incorporate at their front-end an EMIfilter, which is referred to in this specification as a power linefilter.

A very common load for a power line filter is a switching power supply.A switching power supply is generally small in size, of light weight,and operates at high efficiency. In view of these advantages, aswitching power supply is often preferred for electronic devices. It iswell known, however, that harmful high order harmonic noises are inducedfrom a switching transistor, a rectifying diode, a transformer, a chokecoil or the like in normal operation of a switching power supply,potentially causing interference either with operation of a devicepowered by the switching power supply or interfering with the operationsof other nearby devices. Such noises include both differential modenoise which flows between power lines (i.e., between a live line and aneutral line) and common mode noise which flows between a power line anda ground line. Such current noises, connected without filtering directlyto power mains, represent additional high frequency current drains outof the mains. These noise currents cause a voltage drop at the sourceimpedance of the mains which can be measured at the mains terminals.

To attenuate both the differential mode noise and the common mode noise,a power line filter is imposed between the power mains and a load. Overtime, however, due to normal wear and tear and also due to changes inload conditions imposed by usage, load impedance values can change,reflecting impedance mismatches back through the filter, changing theoperating characteristics of the filter and decreasing filterperformance. Current power line filter design topologies are such thatany post-design adjustment of the filter transfer function and/orresonance requires a physical modification of its circuit components.

SUMMARY OF THE INVENTION

Methods, apparatus, and products are disclosed for tuning a programmablepower line filter, the power line filter including a live line, aneutral line, and a ground line connected to input terminals of thefilter on an input side of the filter, the live line and the neutralline connected through inductors in the filter to output terminals on anoutput side of the filter, X-capacitors selectably connected throughtuning switches between the live line and the neutral line, Y-capacitorsselectably connected through tuning switches between the live line andground and/or between the neutral line and ground, and a tuning controlcircuit connected to the tuning switches and selectably connectedthrough one or more programming switches to the load, includingmeasuring by the tuning control circuit the input impedance of the loadand programming by the tuning control circuit the tuning switches independence upon the input impedance of the load.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescriptions of example embodiments of the invention as illustrated inthe accompanying drawings wherein like reference numbers generallyrepresent like parts of example embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-2 set forth schematic diagrams of an example programmable powerline filter that is tunable according to embodiments of the presentinvention.

FIGS. 3-6 set forth flow charts illustrating example methods of tuning aprogrammable power line filter according to embodiments of the presentinvention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

Example embodiments of a programmable power line filter, methods oftuning a programmable power line filter, and computer program productsfor tuning a programmable power line filter in accordance with thepresent invention are described with reference to the accompanyingdrawings, beginning with FIG. 1. FIG. 1 sets forth a schematic diagramof an example programmable power line filter (100) that is tunableaccording to embodiments of the present invention. Except for the load(126), all the items illustrated in FIG. 1 are components of the filter(100).

The filter (100) of FIG. 1 includes a live line (102), a neutral line(104), and a ground line (106) all of which are connected to inputterminals (IT1, IT2, IT3) of the filter on an input side (108) of thefilter. The live line (102) and the neutral line (104) are connectedthrough inductors (L1, L2, L3, L4) in the filter to output terminals(OT1, OT2) on an output side (110) of the filter.

The example filter (100) of FIG. 1 includes two inductors (L1, L3)disposed in the live line (102) between input terminal (IT1) and outputterminal (OT1). The filter also includes two inductors (L2, L4) disposedin the neutral line (104) between input terminal (IT2) and outputterminal (OT2). The inductors (L1, L2, L3, L4) are filter chokes. L3 andL4 are current compensated chokes, wound so that no magnetic field isgenerated by the operating current (50- or 60 Hz)—so L3 and L4 actagainst common-mode noise—with no effect upon the overall operatingcurrent flowing through the filter. L1 and L2 are not currentcompensated—so that they act against differential mode noise.

The filter includes four X-capacitors, called ‘X-capacitors’ becausethey are connected ‘across’ between the live line (102) and the neutralline (104), they also act to suppress differential mode noise. Two ofthe X-capacitors (CX1, CX2) are selectably connected through a firsttuning switch (S1) between the live line (102) and the neutral line(104) on the input side (108) of the inductors (L1, L2, L3, L4), and theother two X-capacitors (CX3, CX4) are selectably connected through asecond tuning switch (S2) between the live line (102) and the neutralline (104) on the output side (110) of the inductors (L1, L2, L3, L4).Each of the switches (S1, S2) in this example is composed of twotransistors, respectively (T1, T2) and (T3, T4), configured aselectronic switches capable of selecting for connection either one orboth of a pair of X-capacitors. Transistors (T1, T2) in switch S1 canconnect across between the live line and the neutral line only capacitorCX1, only capacitor CX2, or both capacitors CX1 and CX2. Transistors(T3, T4) in switch S2 can connect across between the live line and theneutral line only capacitor CX3, only capacitor CX4, or both capacitorsCX3 and CX4.

The filter also includes four line-bypass or ‘Y-capacitors,’ which alsosuppress common mode noise. Two of the Y-capacitors (CY1, CY2) areselectably connected through a third tuning switch (S3) between the liveline (102) and ground (142) on the output side (110) of the inductors(L1, L2, L3, L4), and the other two Y-capacitors are selectablyconnected through a fourth tuning switch (S4) between the neutral line(104) and ground (142)—also on the output side (110) of the inductors(L1, L2, L3, L4). Each of the switches (S3, S4) in this example iscomposed of two transistors, respectively (T5, T6) and (T7, T8),configured as electronic switches capable of selecting for connectioneither one or both of a pair of Y-capacitors. Transistors (T5, T6) inswitch S3 can connect between the live line (102) and ground (142) onlycapacitor CY1, only capacitor CY2, or both capacitors CY1 and CY2.Transistors (T7, T8) in switch S4 can connect between the neutral line(104) and ground (142) only capacitor CY3, only capacitor CY4, or bothcapacitors CY3 and CY4.

The example programmable power line filter (100) of FIG. 1 includes atuning control circuit (112). The tuning control circuit is connectedthrough tuning control bus (134) to the tuning switches (S1, S2, S3, S4)and selectably connected through one or more programming switches (S5,S6, S7) to the load (126). The tuning control circuit (112) is composedof synchronous and asynchronous logic circuitry configured to carry outoverall control of the process of tuning a programmable power linefilter. More particularly, the tuning control circuit (122) isconfigured to tune the filter by measuring the input impedance Z_(i) ofthe load (126) and programming the tuning switches (S1, S2, S3, S4) independence upon the input impedance of the load. The tuning controlcircuit may be implemented as an application specific integrated circuit(‘ASIC’), as programmable array logic (‘PAL’), as a field programmablegate array (‘FPGA’), as a complex programmable logic device (‘CPLD’), asan embedded microcontroller with a control program stored in a Harvardarchitecture, as a microprocessor with a control program stored innon-volatile computer memory (‘tuning memory’), and in other ways thatmay occur to those of skill in the art. To the extent that the tuningcontrol circuit is implemented as PAL, ASIC, FPGA, CPLD, or the like,its functions can be specified in a hardware description language suchas Verilog or in the very high speed integrated circuit designdescription language (‘VHDL’). Such specifications of the tuning controlcircuit in hardware description languages may be embodied in computerprogram products—as can control programs for microcontrollers ormicroprocessors written in machine language, assembler, or in otherprogramming languages as will occur to those of skill in the art.

In the example of FIG. 1, the filter's tuning control circuit (112) isconfigured with load input impedance values associated with switchconfigurations for the tuning switches (124). Configuring the tuningcontrol circuit with load input impedance values associated with switchconfigurations for the tuning switches may be carried out duringmanufacture of the power line filter and left unchanged during theoperational life of the power line filter. Alternatively, theconfiguration of the load input impedance values associated with switchconfigurations for the tuning switches can be updated by data input tothe tuning control circuit periodically during the life of the powerline filter so that, for example, the design parameters of the powerline filter can be changed during the operational life of the filter.The tuning control circuit (112) can be configured with load inputimpedance values associated with switch configurations for the tuningswitches (124) in the form illustrated, for example, by Table 1.

TABLE 1 Load Input Impedance Values Associated With SwitchConfigurations Load Input Impedance Values Switch Configurations Z₁10101010 Z₂ 01101010 Z₃ 11101010 Z₄ 10101010 Z₅ 10011010 Z₆ 10111010 . .. . . . Z₈₁ 11111111

The use of a table to illustrate associations between load inputimpedance values and switch configurations for the tuning switches isonly for convenience of explanation, not a limitation of the presentinvention. Associations between load input impedance values and switchconfigurations for the tuning switches can be implemented with linkedlists, data arrays, and with other data structures as will occur tothose of skill in the art. The impedance values in the left column ofTable 1, Z₁, Z₂, Z₃, and so on, can be specified in polar form with aresultant value and an angle, as a combination of a real value and animaginary component, and so on, as will occur to those of skill in theart. In the filter of FIG. 2, with four tuning switches (S1, S2, S3, S4)each of which can be placed into three useful states, there are 3⁴=81useful switch configurations and therefore 81 different tunings of theprogrammable filter (100). Each record in Table 1 associates an inputimpedance value of the load (126) with a switch configuration. Thetuning control circuit (112), having measured the actual input impedanceZ_(i) of the load (126), can then program the switches by selecting aswitch configuration from Table 1 in dependence upon the switchconfiguration's associated load input impedance value and the measuredinput impedance of the load. That is, the tuning control circuit canlook up in Table 1 a record whose load input impedance value Z₁, Z₂, Z₃,and so on, corresponds to the actual measured value of the inputimpedance Z_(i) of the load and select the associated switchconfiguration.

The measured input impedance need not be exactly equal to any of theconfigured load input impedance values. The tuning control circuit canselect a configured value closest to the measured value of the loadinput impedance. The tuning control circuit can then program the tuningswitches (S1, S2, S3, S4) by setting the switches according to theselected switch configuration.

The switch configurations are represented here as 8-digit binary orlogical values of the eight tuning lines that make up the tuning controlbus (134), one digit for each line in the bus (134), with a ‘1’indicating that a corresponding tuning switch transistor is on and a ‘0’indicating that a corresponding tuning switch transistor is off, sothat:

-   -   Switch configuration 10101010 indicates the tuning switches        configured so that:        -   transistor T1 is on, transistor T2 is off,        -   transistor T3 is on, transistor T4 is off,        -   transistor T5 is on, transistor T6 is off,        -   transistor T7 is on, transistor T8 is off,    -   Switch configuration 01101010 indicates the tuning switches        configured so that:        -   transistor T1 is off, transistor T2 is on,        -   transistor T3 is on, transistor T4 is off,        -   transistor T5 is on, transistor T6 is off,        -   transistor T7 is on, transistor T8 is off,    -   Switch configuration 11101010 indicates the tuning switches        configured so that:        -   transistor T1 is on, transistor T2 is on,        -   transistor T3 is on, transistor T4 is off,        -   transistor T5 is on, transistor T6 is off,        -   transistor T7 is on, transistor T8 is off,    -   Switch configuration 10101010 indicates the tuning switches        configured so that:        -   transistor T1 is on, transistor T2 is off,        -   transistor T3 is on, transistor T4 is off,        -   transistor T5 is on, transistor T6 is off,        -   transistor T7 is on, transistor T8 is off,    -   Switch configuration 10011010 indicates the tuning switches        configured so that:        -   transistor T1 is on, transistor T2 is off,        -   transistor T3 is off, transistor T4 is on,        -   transistor T5 is on, transistor T6 is off,        -   transistor T7 is on, transistor T8 is off,    -   Switch configuration 10111010 indicates the tuning switches        configured so that:        -   transistor T1 is on, transistor T2 is off,        -   transistor T3 is on, transistor T4 is on,        -   transistor T5 is on, transistor T6 is off,        -   transistor T7 is on, transistor T8 is off, and    -   Switch configuration 11111111 indicates the tuning switches        configured so that:        -   transistor T1 is on, transistor T2 is on,        -   transistor T3 is on, transistor T4 is on,        -   transistor T5 is on, transistor T6 is on,        -   transistor T7 is on, transistor T8 is on.

In the programmable power line filter (100) of FIG. 1, the tuningcontrol circuit (112) includes a tuning processor (116) operably coupledthrough a data bus (128) to a pulse generator (116) and to a digitalsignal processor (‘DSP’) (120). The bus (128), referred to in thisspecification as a ‘data bus,’ carries both information among thecomponents of the tuning control circuit as well as instructions fromthe tuning processor to other components. The tuning processor may beimplemented in a number of ways, as a general purpose computermicroprocessor, as an embedded microcontroller, and so on, as will occurto those of skill in the art. The pulse generator is a circuit moduleconfigured to emit, when instructed to do so, a single tuning pulse withpredetermined pulse characteristics, voltage level, duration, and so on.The DSP is a kind of small computer in itself, with internal programmingto sample input voltages, determine time rate of change of the sampledvoltages, and use the time rate of change to calculate an inputimpedance value of the load. With this configuration, the tuning controlcircuit (112) can measure the input impedance of the load by connecting,under control of the tuning processor (116), an output (136) of the load(136) to an input (138) of the DSP (120).

In this example, the filter includes three programming switches (S5, S6,S7), with all three programming switch shown in the same state, witheach of their switch poles thrown to a contact on the left, effectivelyconfiguring the filter to operate in a programming mode. The tuningcontrol circuit can be configured to place the filter in thisprogramming mode upon a manual instruction to do so, ever time thefilter is powered on, periodically according to a predeterminedschedule, and so on as may occur to those of skill in the art. In thisstate, the programming mode, switch S5 disconnects the live line (102)from the load (126) and connects the load to the output (140) of thepulse generator (118). Switch S6 disconnects the load from the neutralline (103). And switch S7 connects an output (136) of the load to atuning resistor R1. The tuning processor (116) instructs the pulsegenerator (118) through bus (128) to drive a tuning pulse (130) from thepulse generator through the load (126). The tuning processor (116) alsoinstructs the DSP (120) to sample the tuning pulse as voltage values(132) output from the load. The DSP uses the sampled voltage values(132) to derive the input impedance Z, of the load (126).

The tuning switch configuration implemented as logical or voltage valueson the signal lines of the tuning control bus (134) can be latched intoplace so long as power is applied to the tuning control circuit (112).When power is cycled off and on again, however, the tuning controlcircuit loses state, requiring the switch configuration for the tuningswitches (S1, S2, S3, S4) to be re-established. One way to do that is toconfigure the tuning control circuit (112) to re-measure the inputimpedance of the load and re-program the tuning switches every timepower to the filter is cycled off and on.

Alternatively, there is at least one more way to re-establish a switchconfiguration for the tuning switches: In the programmable power linefilter (100) of FIG. 1, the tuning control circuit (112) includes tuningmemory (114) operably coupled through the data bus ( ) to the tuningprocessor (116), and all or at least part of the tuning memory (114) isnon-volatile. After measuring the input impedance of the load asdescribed above, the tuning processor (116) can store the measured inputimpedance (122) of the load (126) in a non-volatile portion of thetuning memory (114). Then later, when power to the filter (100) iscycled off and then on again, the tuning processor can use the storedinput impedance (122) of the load to program the tuning switches with noneed to re-measure the input impedance of the load. The tuning processorcan, by use of the stored load input impedance (122), look up a switchconfiguration for the tuning switches among stored associations of loadinput impedance values and switch configurations for the tuning switches(124) in, for example, a data structure similar to Table 1, set thetuning switch transistors on and off according to the selected switchconfiguration, and latch the state of the tuning control bus (134)—allwith no need to re-measure the actual input impedance of the load everytime power to the filter is cycled off and on.

The arrangement of electronic components and other devices making up theexample power line filter (100) illustrated in FIG. 1 are forexplanation, not for limitation of the present invention. Power linefilters capable of being tuned according to various embodiments of thepresent invention may include additional switches, transistors, diodes,capacitors, inductors, amplifiers, control circuitry, and other devices,not shown in FIG. 1, as will occur to those of skill in the art. Variousembodiments of the present invention may be implemented in a variety ofhardware configurations and with various forms of software in additionto those illustrated and described in the example of FIG. 1.

As mentioned, the programming switches (S5, S6, S7) in the example ofFIG. 1, effectively configure the filter in a programming mode. Forcompleteness of explanation, therefore, FIG. 2 sets forth a schematicdiagram of a the example programmable power line filter (100) of FIG. 1with its programming switches (S5, S6, S7) set to configure the filterin a normal operating mode. That is, the programming switches (S5, S6,S7) in the example of FIG. 2 are set to connect the live line (102) andthe neutral line (104) to the load (126) and to disconnect the pulsegenerator (118) and the DSP (120) from the load. The tuning controlcircuit (128) has already tuned the filter by measuring the inputimpedance Z_(i) of the load (126) and programming the tuning switches(S1, S2, S3, S4) in dependence upon the input impedance of the load—sothat the programmable power line filter (100) in this normal operatingmode suppresses common mode noise and differential mode noise from thecurrent supplied to the load (126) through the live line (102) and theneutral line (104).

For further explanation, FIG. 3 sets forth a flow chart illustrating anexample method of tuning a programmable power line filter according toembodiments of the present invention. Tuning a programmable power linefilter according to the method of FIG. 3 is carried out with aprogrammable power line filter like the one illustrated and describedabove with regard to FIG. 1—with a live line, a neutral line, a groundline, inductors, X-capacitors, Y-capacitors, tuning switches,programming switches, and a tuning control circuit—all disposed withrespect to one another as shown and described above with reference toFIG. 1. The method of FIG. 3 therefore is described here with referenceboth to FIG. 3 and also to FIG. 1, using reference numbers from bothfigures.

The method of FIG. 3 includes configuring (202) the tuning controlcircuit (112) with load input impedance values associated with switchconfigurations for the tuning switches (124). Configuring (202) thetuning control circuit (112) with load input impedance values associatedwith switch configurations for the tuning switches (124) can be carriedout as described above with regard to Table 1, using a table as such, alinked list, a two-dimensional array, or other similar data structures,and storing the associations hardwired, in non-volatile memory of thetuning control circuit, or the like. The method of FIG. 3 also includesmeasuring (204) by the tuning control circuit the input impedance (122)of the load (126), accomplished in this example by use of a tuning pulseand voltages sampled by a DSP from an output of the load. The method ofFIG. 3 also includes programming (106) by the tuning control circuit thetuning switches (S1, S2, S3, S4) in dependence upon the input impedance(122) of the load. In the example of FIG. 3, programming (106) thetuning switches includes selecting (208) a switch configuration (e.g.,from the right column of Table 1) in dependence upon the switchconfiguration's associated load input impedance value (left column ofTable 1) and the measured input impedance (122) of the load and setting(210) the tuning switches according to the selected switchconfiguration.

For further explanation, FIG. 4 sets forth a flow chart illustrating afurther example method of tuning a programmable power line filteraccording to embodiments of the present invention. The method of FIG. 4is similar to the method of FIG. 3 in that tuning a programmable powerline filter according to the method of FIG. 4 is carried out with aprogrammable power line filter like the one illustrated and describedabove with regard to FIG. 1—with a live line, a neutral line, a groundline, inductors, X-capacitors, Y-capacitors, tuning switches,programming switches, and a tuning control circuit—all disposed withrespect to one another as shown and described above with reference toFIG. 1. The method of FIG. 3 therefore is described here with referenceboth to FIG. 3 and also to FIG. 1, using reference numbers from bothfigures. The method of FIG. 4 is further similar to the method of FIG. 3in that method of FIG. 4 includes configuring (202) the tuning controlcircuit (112) with load input impedance values associated with switchconfigurations for the tuning switches (124), measuring (204) by thetuning control circuit the input impedance (122) of the load (126), andprogramming (106) by the tuning control circuit the tuning switches (S1,S2, S3, S4) in dependence upon the input impedance (122) of the load. Inthe method of FIG. 4, however, measuring (204) the input impedance ofthe load includes driving (212) by the tuning control circuit a tuningpulse (123) through the load, sampling (214) by the tuning controlcircuit voltage values of the tuning pulse as output from the load, andderiving (216) by the tuning control circuit, in dependence upon thesampled voltage values the input impedance of the load.

For further explanation, FIG. 5 sets forth a flow chart illustrating afurther example method of tuning a programmable power line filteraccording to embodiments of the present invention. The method of FIG. 5is similar to the method of FIG. 3 in that tuning a programmable powerline filter according to the method of FIG. 5 is carried out with aprogrammable power line filter like the one illustrated and describedabove with regard to FIG. 1—with a live line, a neutral line, a groundline, inductors, X-capacitors, Y-capacitors, tuning switches,programming switches, and a tuning control circuit—all disposed withrespect to one another as shown and described above with reference toFIG. 1. The method of FIG. 3 therefore is described here with referenceboth to FIG. 3 and also to FIG. 1, using reference numbers from bothfigures. The method of FIG. 5 is further similar to the method of FIG. 3in that method of FIG. 5 includes configuring (202) the tuning controlcircuit (112) with load input impedance values associated with switchconfigurations for the tuning switches (124), measuring (204) by thetuning control circuit the input impedance (122) of the load (126), andprogramming (106) by the tuning control circuit the tuning switches (S1,S2, S3, S4) in dependence upon the input impedance (122) of the load. Inthe method of FIG. 5, however, the tuning control circuit (112) includesa tuning processor (116) operably coupled through a data bus (128) to apulse generator (118) and to a DSP (120). Also in the method of FIG. 5,measuring (204) the input impedance of the load includes connecting(218), by the tuning processor, an output (136) of the load (126) to aninput (138) of the DSP (120), driving (220) a tuning pulse (123, 130)from the pulse generator (118) through the load (126), sampling (222)the tuning pulse (123, 132) by the DSP (120) as voltage values outputfrom the load (126), deriving (224) by the DSP (120) the input impedance(122) of the load in dependence upon the sampled voltage values, andproviding (226) the input impedance (122) of the load by the DSP (120)to the tuning processor (116).

For further explanation, FIG. 6 sets forth a flow chart illustrating afurther example method of tuning a programmable power line filteraccording to embodiments of the present invention. The method of FIG. 6is similar to the method of FIG. 3 in that tuning a programmable powerline filter according to the method of FIG. 6 is carried out with aprogrammable power line filter like the one illustrated and describedabove with regard to FIG. 1—with a live line, a neutral line, a groundline, inductors, X-capacitors, Y-capacitors, tuning switches,programming switches, and a tuning control circuit—all disposed withrespect to one another as shown and described above with reference toFIG. 1. The method of FIG. 3 therefore is described here with referenceboth to FIG. 3 and also to FIG. 1, using reference numbers from bothfigures. The method of FIG. 6 is further similar to the method of FIG. 3in that method of FIG. 6 includes configuring (202) the tuning controlcircuit (112) with load input impedance values associated with switchconfigurations for the tuning switches (124), measuring (204) by thetuning control circuit the input impedance (122) of the load (126), andprogramming (106) by the tuning control circuit the tuning switches (S1,S2, S3, S4) in dependence upon the input impedance (122) of the load. Inthe method of FIG. 6, however, the tuning control circuit (112) includesa tuning memory (114), at least some portion of which is non-volatilememory, with the tuning memory (114) coupled through a data bus (128) tothe tuning processor (116). The method of FIG. 6 also includes storing(228), by the tuning processor (116) in the non-volatile tuning memory(114), the measured input impedance (122) of the load. Also in themethod of FIG. 6, programming (206) the tuning switches includesprogramming (230) the tuning switches by the tuning processor (116) independence upon the stored input impedance (122) of the load withoutremeasuring the input impedance of the load when power to the power linefilter (100) is cycled off and on.

In view of the explanations set forth above, readers will recognize thatthe benefits of tuning a programmable power line filter according toembodiments of the present invention include adjusting the operatingcharacteristics, the resonant response, characteristic impedance,transfer function, pole locations, and so on, of a programmable powerline filter quickly and automatically without physical substitution ofcircuit elements.

Example embodiments of the present invention are described largely inthe context of a fully functional computer system for tuning aprogrammable power line filter. Readers of skill in the art willrecognize, however, that the present invention also may be embodied in acomputer program product disposed upon computer readable storage mediafor use with automated programmable power line filters. Such computerreadable storage media may be any storage medium for machine-readableinformation, including magnetic media, optical media, or other suitablemedia. Examples of such media include magnetic disks in hard drives ordiskettes, compact disks for optical drives, magnetic tape, and othersas will occur to those of skill in the art. Persons skilled in the artwill immediately recognize that any computer system having suitableprogramming means will be capable of executing the steps of the methodof the invention as embodied in a computer program product. Personsskilled in the art will recognize also that, although some of theexample embodiments described in this specification are oriented tosoftware installed and executing on computer hardware such as a tuningprocessor in a power line filter, nevertheless, alternative embodimentsimplemented as firmware or as hardware are well within the scope of thepresent invention.

It will be understood from the foregoing description that modificationsand changes may be made in various embodiments of the present inventionwithout departing from its true spirit. The descriptions in thisspecification are for purposes of illustration only and are not to beconstrued in a limiting sense. The scope of the present invention islimited only by the language of the following claims.

What is claimed is:
 1. A method of tuning a programmable power linefilter, the power line filter comprising: a live line, a neutral line,and a ground line connected to input terminals of the filter on an inputside of the filter, the live line and the neutral line connected throughinductors in the filter to output terminals on an output side of thefilter; at least one inductor disposed in the live line between theinput terminals and the output terminals, this at least one inductorcharacterized by an input side and an output side; at least one inductordisposed in the neutral line between the input terminals and the outputterminals, this at least one inductor also characterized by an inputside and an output side; a plurality of X-capacitors selectablyconnected through a first tuning switch between the live line and theneutral line on the input side of the inductors; a plurality ofX-capacitors selectably connected through a second tuning switch betweenthe live line and the neutral line on the output side of the inductors;a plurality of Y-capacitors selectably connected through a third tuningswitch between the live line and ground on the output side of theinductors; a plurality of Y-capacitors selectably connected through afourth tuning switch between the neutral line and ground on the outputside of the inductors; and a tuning control circuit connected to thetuning switches and selectably connected through one or more programmingswitches to a load; the method comprising: measuring by the tuningcontrol circuit an input impedance of the load; and programming by thetuning control circuit the tuning switches in dependence upon the inputimpedance of the load.
 2. The method of claim 1 further comprisingconfiguring the tuning control circuit with load input impedance valuesassociated with switch configurations for the tuning switches.
 3. Themethod of claim 1 further comprising: configuring the tuning controlcircuit with load input impedance values associated with switchconfigurations for the tuning switches; wherein programming the tuningswitches further comprises: selecting a switch configuration independence upon the switch configuration's associated load inputimpedance value and the measured input impedance of the load; andsetting the tuning switches according to the selected switchconfiguration.
 4. The method of claim 1 wherein measuring the inputimpedance of the load further comprises deriving, from sampled voltagevalues of a tuning pulse driven from the tuning control circuit throughthe load, the input impedance of the load.
 5. The method of claim 1wherein measuring the input impedance of the load further comprises:driving by the tuning control circuit a tuning pulse through the load;sampling by the tuning control circuit voltage values of the tuningpulse as output from the load; and deriving by the tuning controlcircuit, in dependence upon the sampled voltage values the inputimpedance of the load.
 6. The method of claim 1 wherein the tuningcontrol circuit further comprises a tuning processor operably coupledthrough a data bus to a pulse generator and to a digital signalprocessor (‘DSP’), and measuring the input impedance of the load furthercomprises: connecting, by the tuning processor, an output of the load toan input of the DSP; driving a tuning pulse from the pulse generatorthrough the load; sampling the tuning pulse by the DSP as voltage valuesoutput from the load; deriving by the DSP the input impedance of theload in dependence upon the sampled voltage values; and providing theinput impedance of the load by the DSP to the tuning processor.
 7. Themethod of claim 1 wherein: the tuning control circuit further comprisesa tuning processor operably coupled through a data bus to non-volatiletuning memory; the method further comprises storing, by the tuningprocessor in the non-volatile tuning memory, the measured inputimpedance of the load; and programming the tuning switches furthercomprises programming the tuning switches by the tuning processor independence upon the stored input impedance of the load withoutremeasuring the input impedance of the load when power to the power linefilter is cycled off and on.
 8. A programmable power line filtercomprising: a live line, a neutral line, and a ground line connected toinput terminals of the filter on an input side of the filter, the liveline and the neutral line connected through inductors in the filter tooutput terminals on an output side of the filter; at least one inductordisposed in the live line between the input terminals and the outputterminals, this at least one inductor characterized by an input side andan output side; at least one inductor disposed in the neutral linebetween the input terminals and the output terminals, this at least oneinductor also characterized by an input side and an output side; aplurality of X-capacitors selectably connected through a first tuningswitch between the live line and the neutral line on the input side ofthe inductorsf; a plurality of X-capacitors selectably connected througha second tuning switch between the live line and the neutral line on theoutput side of the inductors; a plurality of Y-capacitors selectablyconnected through a third tuning switch between the live line and groundon the output side of the inductors; a plurality of Y-capacitorsselectably connected through a fourth tuning switch between the neutralline and ground on the output side of the inductors; and a tuningcontrol circuit connected to the tuning switches and selectablyconnected through one or more programming switches to a load, the tuningcontrol circuit configured to tune the filter by measuring an inputimpedance of the load and programming the tuning switches in dependenceupon the input impedance of the load.
 9. The filter of claim 8 furthercomprising the tuning control circuit configured with load inputimpedance values associated with switch configurations for the tuningswitches.
 10. The filter of claim 8 wherein the tuning control circuitis configured with load input impedance values associated with switchconfigurations for the tuning switches, and programming the tuningswitches further comprises: selecting a switch configuration independence upon the switch configuration's associated load inputimpedance value and the measured input impedance of the load; andsetting the tuning switches according to the selected switchconfiguration.
 11. The filter of claim 8 wherein measuring the inputimpedance of the load further comprises deriving, from sampled voltagevalues of a tuning pulse driven from the tuning control circuit throughthe load, the input impedance of the load.
 12. The filter of claim 8wherein measuring the input impedance of the load further comprises:driving by the tuning control circuit a tuning pulse through the load;sampling by the tuning control circuit voltage values of the tuningpulse as output from the load; and deriving by the tuning controlcircuit, in dependence upon the sampled voltage values the inputimpedance of the load.
 13. The filter of claim 8 wherein the tuningcontrol circuit further comprises a tuning processor operably coupledthrough a data bus to a pulse generator and to a digital signalprocessor (‘DSP’), and measuring the input impedance of the load furthercomprises: connecting, by the tuning processor, an output of the load toan input of the DSP; driving a tuning pulse from the pulse generatorthrough the load; sampling the tuning pulse by the DSP as voltage valuesoutput from the load; deriving by the DSP the input impedance of theload in dependence upon the sampled voltage values; and providing theinput impedance of the load by the DSP to the tuning processor.
 14. Thefilter of claim 8 wherein: the tuning control circuit further comprisesa tuning processor operably coupled through a data bus to non-volatiletuning memory; the tuning control circuit is further configured to tunethe filter by storing, by the tuning processor in the non-volatiletuning memory, the measured input impedance of the load; and programmingthe tuning switches further comprises programming the tuning switches bythe tuning processor in dependence upon the stored input impedance ofthe load without remeasuring the input impedance of the load when powerto the power line filter is cycled off and on.
 15. A computer programproduct for tuning a programmable power line filter, the power linefilter comprising: a live line, a neutral line, and a ground lineconnected to input terminals of the filter on an input side of thefilter, the live line and the neutral line connected through inductorsin the filter to output terminals on an output side of the filter; atleast one inductor disposed in the live line between the input terminalsand the output terminals, this at least one inductor characterized by aninput side and an output side; at least one inductor disposed in theneutral line between the input terminals and the output terminals, thisat least one inductor also characterized by an input side and an outputside; a plurality of X-capacitors selectably connected through a firsttuning switch between the live line and the neutral line on the inputside of the inductor; a plurality of X-capacitors selectably connectedthrough a second tuning switch between the live line and the neutralline on the output side of the inductors; a plurality of Y-capacitorsselectably connected through a third tuning switch between the live lineand ground on the output side of the inductors; a plurality ofY-capacitors selectably connected through a fourth tuning switch betweenthe neutral line and ground on the output side of the inductors; and atuning control circuit connected to the tuning switches and selectablyconnected through one or more programming switches to a load; thecomputer program product disposed in a computer-readable recordingmedium, the computer program product comprising computer programinstructions capable, when executed, of causing the tuning controlcircuit to tune the filter by measuring an input impedance of the loadand programming the tuning switches in dependence upon the inputimpedance of the load.
 16. The computer program product of claim 15wherein the tuning control circuit is configured with load inputimpedance values associated with switch configurations for the tuningswitches.
 17. The computer program product of claim 15 wherein thetuning control circuit is configured with load input impedance valuesassociated with switch configurations for the tuning switches andprogramming the tuning switches further comprises: selecting a switchconfiguration in dependence upon the switch configuration's associatedload input impedance value and the measured input impedance of the load;and setting the tuning switches according to the selected switchconfiguration.
 18. The computer program product of claim 15 whereinmeasuring the input impedance of the load further comprises: driving bythe tuning control circuit a tuning pulse through the load; sampling bythe tuning control circuit voltage values of the tuning pulse as outputfrom the load; and deriving by the tuning control circuit, in dependenceupon the sampled voltage values the input impedance of the load.
 19. Thecomputer program product of claim 15 wherein the tuning control circuitfurther comprises a tuning processor operably coupled through a data busto a pulse generator and to a digital signal processor (‘DSP’), andmeasuring the input impedance of the load further comprises: connecting,by the tuning processor, an output of the load to an input of the DSP;driving a tuning pulse from the pulse generator through the load;sampling the tuning pulse by the DSP as voltage values output from theload; deriving by the DSP the input impedance of the load in dependenceupon the sampled voltage values; and providing the input impedance ofthe load by the DSP to the tuning processor.
 20. The computer programproduct of claim 15 wherein: the tuning control circuit furthercomprises a tuning processor operably coupled through a data bus tonon-volatile tuning memory; the computer program product furthercomprises computer program instructions capable, when executed, ofcausing the tuning control circuit to tune the filter by storing, by thetuning processor in the non-volatile tuning memory, the measured inputimpedance of the load; and programming the tuning switches furthercomprises programming the tuning switches by the tuning processor independence upon the stored input impedance of the load withoutremeasuring the input impedance of the load when power to the power linefilter is cycled off and on.